Gas Storage System

ABSTRACT

Among other things, a gas storage system includes a group of capsules and an activation element coupled to the group. The group of capsules are formed within a substrate and contain gas stored at a relatively high pressure compared to atmospheric pressure. The activation element is configured to deliver energy in an amount sufficient to cause at least one of the capsules to release stored gas.

PRIORITY CLAIM

This application is a continuation (and claims the benefit of priorityunder 35 USC 120) of U.S. application Ser. No. 14/055,992 filed Oct. 17,2013, which is a continuation of application Ser. No. 12/645,263, filedDec. 22, 2009, which claims priority from U.S. Provisional Application61/140,349, filed Dec. 23, 2008. The disclosure of the priorapplications is considered part of (and is incorporated by reference in)the disclosure of this application.

BACKGROUND

This disclosure relates to a gas storage system.

Fuel cells are devices that produce power by electrochemically reactinga fuel with an oxidizer. Fuel cell systems are of interest because theygenerally use more energetic fuels than traditional battery chemistries.Fuel cells combined with a fuel subsystem, may produce a batteryreplacement device that has more stored energy and in turn provides asignificantly longer run time. It is desirable to make the volumetricand/or gravimetric energy densities of the entire battery replacementdevice significantly exceed that of the battery that it replaces. Ingeneral, this requires reducing or minimizing the size, weight andcomplexities of the fuel cell and fuel subsystem.

SUMMARY

In one aspect, the disclosure features a gas storage system thatincludes a group of capsules and an activation element coupled to thegroup. The group of capsules are formed within a substrate and containgas stored at a relatively high pressure compared to atmosphericpressure. The activation element is configured to deliver energy in anamount sufficient to cause at least one of the capsules to releasestored gas.

In another aspect, the disclosure features a method for constructing asystem that stores gas. The method includes introducing an amount ofliquefied gas into an assembly chamber, where a device having aplurality of micro-capsules that act as vessel to contain a gas underpressure and a lid substrate are placed. The amount of liquefied gas isselected to provide a predetermined pressure within the capsules afterthe liquefied gas transitions to a gaseous state. The method alsoincludes bonding the lid substrate to the capsules to seal the gasinside the capsules.

In another aspect, the disclosure features a system for digitallycontrolled release of a fluid. The system includes a substrate. Thesubstrate includes groups of fluid-filled capsules coupled to activationelements control circuitry configured to deliver a control signal to aselected activation element. The control signal causes the selectedactivation element to rupture a corresponding group of fluid-filledcapsules to release fluid in the corresponding group to a device thataccepts the fluid.

In another aspect, the disclosure features a fuel cell system fordelivering power to one or more electronic devices. The fuel cell systemincludes a fuel cell element and fuel source. The fuel source includes asubstrate that includes groups of gas-filled capsules coupled toactivation elements and control circuitry configured to deliver acontrol signal to a selected activation element. The control signalcauses the selected activation element to rupture a corresponding groupof gas-filled capsules to send gas in the corresponding group to thefuel cell element.

In another aspect, the disclosure features a controller for controllingoperation of a gas storage system. The controller includes logiccircuitry to select a group of gas-filled capsules fabricated on asubstrate. The circuitry includes circuitry to determine an address forthe group, including an row count and a column count and circuitry todetermine a substrate count that corresponds to the group of gas filledcapsules.

The digital gas storage (DGS) system is for use with a variety ofapplications, one of which includes a fuel cell system. The DGS systemstores gas at high pressure and releases the gas under digital control.The DGS system may be a stand-alone system or coupled with anothersystem, e.g., a fuel cell, to which it supplies the gas. In someimplementations, the DGS system is coupled with a fuel cell to provide apower generation system. Compared to conventional energy supplies, e.g.,batteries, the power generation system including the fuel cell can havea power per weight an order of magnitude better than most batterychemistries. The DGS system includes an assembly of one or more DGSsubstrates having gas storage components that may be constructed withina silicon substrate on a micro scale.

The DGS system may be combined with a variety of fuel cells. Examples ofwhich include small, lightweight, and high power density fuel cells,such as those described in application Ser. No. 10/985,736, filed Nov.9, 2004, now U.S. Pat. No. 7,029,779, and entitled “Fuel cell and powerchip technology,” the contents of which are incorporated herein byreference in their entirety.

A comparison of the DGS system's expected energy density, when combinedwith a fuel cell like that described in the referenced patent (“PT”), tothat of conventional Li-Ion batteries, shows that the DGS systemprovides a significant improvement both volumetrically andgravimetrically. The details of the comparison are shown below inTable 1. Another advantageous feature of the DGS system is its abilityto be implemented on a sub-millimeter scale, which enables fabricationof novel power systems and other devices.

TABLE 1 Energy storage density comparision. Parameter Li-Ion PT & DGSMultiple Volumetric, Wh/l 350 843 2.4 Gravimetric, Wh/kg 150 1,648 10.9H2 storage, Wt % 8.63%

In addition to providing a substantial amount of stored energy on amicro level, the DGS device can also be used in other applications. Forexample, the DGS device may be used to store an antidote or fluids orsolids. The DGS device can propel items such as a dart or used inconnection with a reconnaissance device or used to deploy sensors. Inanother application, the DGS device may store different gases such ashydrogen or oxygen in different sections or capsules. The DGS device mayprovide buoyancy control to small underwater autonomous vehicles andalternatively may store vacuum.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are perspective and cross-sectional views depicting in ahierarchical manner a digital gas storage (DGS) device.

FIG. 2 is a diagrammatical view of a DGS system.

FIGS. 3A-3B are top views of the DGS substrate's row and columnaddressing.

FIG. 4 is a blown-up top view of a portion of FIG. 3B showing a thermalactivation element for use in the DGS system.

FIG. 5 is a perspective view of the bottom cap substrate of capsules inthe DGS system.

FIG. 6 is a view showing top caps substrate of the capsules from theinside looking upward.

FIGS. 7A-7B are perspective views of the cylindrical shaped interiors ofthe capsules.

FIG. 8 is a flowchart.

FIG. 9 is a block diagram of a master control circuit.

FIG. 10 is a block diagram of a slave control circuit.

FIG. 11 is a schematic cross-sectional view of a cascade configurationof capsules.

FIGS. 12A-12B are enlarged views of portions of the configuration shownin FIG. 11.

DETAILED DESCRIPTION

The DGS system stores a gas at a very high pressure in micro pressurevessels, herein called capsules, formed within a substrate of a hightensile-strength material. Units of the gas are selectively releasedfrom the micro pressure capsules using a digital control, such as thatof a counter, state-machine, controller or processor. For example, insome implementations, the DGS system stores a high pressure hydrogen gasin the pressure capsules formed from single crystal silicon.

Hydrogen gas has a very high gravimetric energy density but does notcompress well. Hydrogen gas is compressed to very high pressures to packin enough hydrogen atoms to start to compete with other energy sourceson a volumetric basis. Commercial hydrogen is stored in tanks at 2,200pounds per square inch (psi). Even at this pressure, which is 150 timesnormal atmospheric pressure, it has less stored energy per unit volumeor weight than a common battery. To achieve high energy densities, suchas those shown in Table 1, the DGS system stores the hydrogen gas atapproximately 17,500 psi, which is about 1,190 times normal atmosphericpressure. The material in which the hydrogen gas is stored has a highstrength to contain the high pressure while minimizing the structuralweight and volume thus achieving high volumetric and gravimetric energydensities.

To hold such a high amount of pressure, with additional considerationfor safety, the DGS system uses crystalline silicon, e.g., singlecrystal silicon, having a theoretical tensile strength of over 1,000,000psi. Tensile strength is a material property that defines the criticalstress applied to the material to cause the material to fracture. Insome embodiments, the DGS pressure capsules contain gases at a pressureof about 17,500 psi. The high pressure exerted on the inner surfaces ofthe capsules generates stresses that are within the ranges of thematerials' tensile strength and leaves a sufficient margin for safety.For safety reasons, the parameters of the DGS system are selected sothat the stresses within the silicon material do not exceed a predefinedsafety threshold. For example, a selection of parameters to provide astorage pressure of 17,500 psi include a micro capsule geometry with adiameter of approximately 50 μm and a minimum wall thickness ofapproximately 1.37 μm. Other parameter values are possible.

A high pressure, e.g., greater than one atmosphere and in particular,about 2,200 psi to about 17,500 psi, can be maintained in the micropressure vessel capsules. In addition, if the safety margin relative tothe tensile strength of the material is reduced, then pressures beyond17,500 psi can also be used.

Referring to FIG. 1A, a DGS device 10 includes at least one or moresubstrates 12 that are functionally divided into sections 14, each ofwhich includes a group of gas-filled micro capsules 14 a, 14 b, . . . ,14 xx. The sections 14 are arranged in a grid format and the capsules 14a, . . . , 14 xx are hexagonally arranged. Other arrangements can alsobe used. Each capsule 14 a, . . . , 14 xx is cylindrical (FIG. 1B) withhemispherical end-caps. The cylindrical section has a circularcross-section exposed in a surface of the substrate 12. Gas, e.g., thehydrogen gas, is stored in each capsules 14 a, . . . , 14 xx, and thegas is sealed in the capsules, via a silicon lid substrate 114 (FIG.1B). Each section 14 (or each capsule) is activated to rupture andrelease gas via slave control electronics 16. The sections 14 areconfigured to release the gas stored in all of the capsules 14 a, . . ., 14 xx in a particular, selected section 14, without releasing thegases stored in capsules of the other sections 14.

As shown, each DGS substrate 12 has a slave control circuit 16 that isresponsible for selecting which of its sections 14 is addressed for gasrelease. There is one master control circuit 20 (FIG. 2) for a DGSdevice 10 that controls the slave control circuits 16 for acorresponding number of DGS substrates 12. The master control circuit 20may be on it's own control chip substrate. In some embodiments, themaster control circuit 20 is on one of the DGS substrates 12. Othercontrol configurations can be provided.

Two or more sections 14 can be activated simultaneously or at differenttimes to release the gases stored in the sections 14. The dimensions andconfigurations of the substrate 12, the sections 14 (includingindividual capsules) and the capsules 14 a, . . . , 14 xx in eachsection 14 can be selected based on desired gas storage and releaseprofiles.

For example, the substrate 12 has dimensions of 1 cm² and a thickness of1 mm. The 1 cm² area is divided into one hundred (100) 1 mm² sections14. Each 1 mm² section 14 includes a group of 378 micro capsules 14 a, .. . , 14 xx packed hexagonally and filled with gas.

Referring to FIG. 1B, one capsule 14 t in the section 14 can have acylindrical body 48 t formed in one or more layers of materials, e.g.,three layers 50 a, 50 b, 50 c. The two ends of the cylindrical body 48 tare capped with a bottom cap 42 t formed in one layer of material 44 anda top cap 46 t formed in another layer of material 47. In addition, thetop cap 42 t includes a port 40 that once exposed to the external regionof the capsule 14 t, allows fluid communication, e.g., gas communicationbetween the external region and the internal of the capsule. The port issealed by a lid 114 formed, e.g., as a layer of material. A thermalactivation element 38 is located on top of the lid above the port. Onceactivated, the heat generated by the activation element 38 ruptures thelid and expose the port 40 to the external region of the capsule. Thestructure and formation of the capsules are described further below.

Referring to FIG. 2, a DGS device 10 includes a control chip substrate20 (FIG. 9) and a DGS system 22 that has one or more DGS substrates 12(see also, FIG. 1A) stacked with the control chip substrate 20. Mastercontrol circuits reside on the control chip 20. The master controlcircuits from control chip substrate 20 send control signals to the DGSsystem 22 to indicate which section(s) (e.g., section 14 of FIGS. 1A) ofwhich DGS substrate(s) 12 to activate. The control chip substrate 20also monitors the pressure of the released gas from the DGS system. Inparticular, the control chip substrate 20 are electronically coupled toslave control electronics 16 on each substrate 12. The control chipsubstrate 20 can include a control circuit, for example, electrodes 26,28, and data control 30, that delivers electronic signals, e.g., datasignals, to desired slave control electronics 16 to activate sections ofthe substrate 12.

The DGS system 22 can have a variety of configurations. For example, themaster control chip substrate 20 and the substrates 12 may be arrangedin configurations other than those shown in FIG. 2. In some embodiments,the control chip substrate 20 and the DGS device 10 reside on separatedevices that are electronically coupled to each other, e.g., via a wiredor wireless connection. In some embodiments, the control chip substrate20 and the DGS device 10 are integrated into the same device, e.g., as acompletely stand-alone device. The slave control electronics 16 canreside on each substrate 12 or can reside on a separate member that iscoupled to the substrate 12. The DGS system 22 may include its own powersupply (not shown) or it may be coupled to an outside power supply (notshown).

Referring to FIGS. 3A-3B, conductors of the slave control electronics 16are arranged in the form of a standard row-column matrix (row conductorlines 32 and column conductor lines 34) and an activation element 38.This portion of the slave electronics has nodes 36 (i.e., an addressline crossovers where a corresponding row conductor line isdielectrically isolated from a crossing column conductor line) locatedwithin the sections 14. From each of the nodes 36 a pair of conductors37 a, 37 b couple their respective row 32 and column 34 conductors to acorresponding activation element 38. Current flow between a row line 32,a row conductor 37 a, through an activation element 38 to acorresponding column conductor 37 b and column conductor line 34completes an electrical circuit (along with the remaining slave controlelectronics discussed below) and allows the activation element 38 togenerate heat and rupture the lid substrate portion of the correspondingsection 14.

The row-column matrix is disposed on top of the substrate 12, e.g., ontop of the lid substrate that seals the capsules, or can be embedded inthe substrate 12. Each section 14 is indexed (e.g., have an addresswithin the substrate 12) based on the location of the correspondingactivation element 38. Based on the addresses, the electronic signals(FIG. 9) delivered from the control chip substrate 20 (FIG. 2) areapplied to the desired section 14 through the selected slave controlcircuit 16. In each section 14, at least one capsule 14 t has its lidcoupled to a thermal activation element 38 connected to the slavecontrol electronics 16. When a particular section 14 on a particularsubstrate is selected by the master control chip substrate 20, the slavecontrol electronics 16 on the particular substrate activates thatsection 14 based on the X row and Y column address. The slave controlelectronics 16 sends a current to the selected section 14, via theappropriate row and column conductors to heat the thermal activationelement 38. When the thermal activation element 38 reaches asufficiently high temperature, it activates the capsules in the selectedsection 14 by locally weakening and rupturing the silicon lids of one ormore capsules in that section to release the sealed hydrogen gas fromthe ruptured capsules. The thermal activation element 38 may be composedof a variety of various conducting materials, for example, tungsten,other metals, or metal alloys. The activation element 38 may alsoinclude a chemical that releases heat and/or pressure by chemicalreaction when electrically triggered by the control electronics 16. Theactivation element 38 may also include an electro-mechanical device torelease the stored gas.

Referring to FIG. 4, one embodiment of the thermal activation element 38has a serpentine shape to cover the cross-section of the capsule 14 tand effectively transfer heat. The dimensions of the serpentine shapeare selected based on the dimensions of the section 14 and capsule 14 t.Other shapes for the element 38 can also be used.

Each capsule has a bottom cap, a top cap and a cylinder body, examplesof which are depicted in FIGS. 1B, 5, 6, and 7A-B. Each component may beformed in a single crystal silicon wafer. Although the dimensions of thecapsules can vary, one such possible set of approximate thicknessdimensions is described below with respect to FIGS. 1B, 5, 6, and 7A-B.

Referring to FIG. 5, arrays of bottom caps 42 a, 42 b, 42 c, . . . , 42xx, are formed in a single crystal silicon member 44. The silicon member44 is about 30 μm thick, and each bottom cap 42 a, . . . , 42 xx ishemispherical having a uniform diameter, e.g., about 50 μm. The siliconmember 44 can include 100s to 1000s of caps. The arrays of bottom capsare isotropically etched into the silicon member 44 in a hexagonalpacking. Other configurations, such as other polygonal configurations,circular configurations, and linear configurations, may be used.

Referring to FIG. 6, similar to the bottom caps of FIG. 5, arrays of topcaps 46 a, 46 b, . . . , 46 xx, are formed in a single crystal siliconmember 47 having a thickness of about 30 μm. In addition, one of the topcaps, 46 p, has a gas fill/release port 40 that connects the interior ofthe capsule to the exterior of the capsule. The port 40 is circular andhas a diameter, e.g., of about 20 μm. The port 40 can have other shapes.In some embodiments, the capsules within one section 14 (FIG. 1A) areinterconnected by small open pathways (not shown) that allow gas to flowamong the capsules. Only selected capsules, e.g., one capsule 46 p,include the port 40 for filling and releasing gases into or out of allof the interconnected capsules. Multiple top caps can have ports likethe port 40. In other embodiments in which a section of capsules arearranged in a cascade configuration (discussed below), each top cap ofthe capsules includes a port 40 (not all shown).

The port(s) 40 are sealed by sealing lid(s) formed in a single crystalsilicon member (FIG. 1B) having a thickness of about 20 μm. As explainedpreviously, part of the control electronics 16 (row and column lineconductors) are fabricated on top of the lid substrate. The controlelectronics can also be formed on top of the lid substrate and areformed prior to the lid substrate being used to seal the capsules.

Referring to FIG. 7B, arrays of cylindrical bodies 48 a, 48 b, . . . ,48 xx are formed in single crystal silicon member 50 having a thicknessof about 900 μm (microns) to about 1000 μm (this is but an exemplaryrange, other ranges are possible). A specific thickness is 940 μm. Ingeneral, the thickness can vary depending on the DGS application. Insome embodiments, each cylindrical body has a diameter of about 50 μmand each 1 mm×1 mm area of the silicon member 50 can include 378cylindrical bodies packed hexagonally. Multiple layers of silicon member50 are stacked to form elongated cylindrical bodies. In the exampleshown in FIG. 7A, three silicon members 50 a, 50 b, 50 c, each havingthe feature of the silicon member 50 of FIG. 7B are stacked so that thecylindrical body 48 a, . . . , 48 xx has a tripled length (see also,FIG. 1B). Any numbers of silicon members 50 can be stacked.

The DSG substrate 12 of FIG. 1A can be formed by stacking the siliconmember 44 carrying the bottom caps, the at least one silicon member 50carrying the cylindrical bodies, the silicon member 47 carrying the topcaps, and the silicon member 114 carrying the sealing lids. The capsules14 a, . . . , 14 xx in each section 14 (FIG. 1A) can have variousconfigurations. In one configuration, the capsules each have a smallopen pathway connected to the other capsules. The pathway can be locatedon the sidewall of each capsule and can be built during the fabricationof the capsules. The pathways provide gas fill/release ways to eachcapsule. For each section 14, only one release port (not shown) isneeded to release the gas in all interconnected capsules in the section.

In some embodiments, the capsules 14 a, . . . , 14 xx are isolated fromeach other (e.g., no interconnecting pathways). Within a section, thesidewall of each capsule is designed thinner than the thickness requiredto contain the high pressure gas if the capsule were standing alone withambient pressure surrounding it. If isolated, a single high pressurefilled capsule surrounded by low ambient pressure would burst. However,when packed together, these capsules are able to hold the storagepressure without having their sidewalls bursting, because the reciprocalforces that the capsules exert on each other's sidewalls balance andcompensate for the thinness in their walls.

In use, the overall strength of the section of capsules is sufficient tohold a storage pressure while the strength of an individual capsule isnot. When the sealing lid of a particular capsule of the section isopened, the pressure within the particular capsule falls to aroundambient. If the minimum wall thickness of the surrounding capsules(adjacent to the particular capsule) is insufficient to allow them tostand alone (17,500 psi inside, ambient outside), the walls betweenthese surrounding capsules and the particular capsule break. The gasesstored in the surrounding capsules is released from the opened lid. Thisprocess will repeat as a cascade failure until the perimeter capsules ofthe section are reached. The gases in the entire section 14 is releasedthrough one open lid. The walls between adjacent sections 14 are builtto the thickness required to hold the pressure so that the cascadefailure within one section 14 does not spread into other sections andgas release in each section 14 can be independently controlled andoperated without affecting other sections 14.

As described above, the mechanism for releasing the gas from a section14 of micro capsules 14 a, . . . , 14 xx is heating the lid of at leastone capsule. The tensile strength of a material is affected bytemperature, i.e., it gets weaker as the temperature goes up. Onlywithin a certain range of temperatures does the single crystal siliconused for the lids of the capsules have a sufficiently high materialstrength to withstand the high gas storage pressure within the capsules.When exposed to temperatures above this range, the tensile strength ofthe silicon lids decreases to the point where the lids rupture andrelease the gas that they contain. The temperature that causes tensilestrength of single crystal silicon to drop below the level required tomaintain the storage pressure is referred to as the “rupturetemperature.” The rupture temperature depends on the geometry of thecapsule's top cap and the sealing lid. For a DGS device includingcapsules having the dimensions shown in FIG. 1A, the rupture temperaturemay be approximately 150° C. At this temperature, the sealing lidruptures, and the gas escapes.

The energy used by the thermal activation element 38 (FIG. 4) to heatthe silicon lids to the point of rupture is called the “activationenergy” and is a parasitic loss of system energy. The loss of the systemenergy is dependent on the configuration of the capsules and can bereduced by heating one capsule and causing call capsules in a section 14to release the stored gases. The activation energy may be expressed asthe percentage of the total stored energy within the section. In somestudies, the activation energy of the DGS device described in FIG. 1Awas calculated to be less than 1%.

Hydrogen molecules are the smallest molecules and are known to permeatethrough all materials given enough time. The rage of permeation can bedetermined, for example, based on the storage material'scharacteristics, temperature and pressure on the hydrogen gas. In someembodiments, at a storage temperature of 500° C., which is higher thanthe temperature of expected use and storage for the DGS device 10, webelieve that it could lose about 1% of the total stored hydrogen afterabout 73 years.

Single crystal silicon is used to construct the pressure capsules andtheir lids due to its high tensile strength, a bulk property, of over1,000,000 psi. Without being bound by theory, is believed that thecrystalline lattice structure of the single crystal silicon provides thehigh tensile strength. Pieces of silicon materials can be bonded, e.g.,via fusion bonding, in such a way as to produce “effectively” a singlepiece. The bulk properties of the single crystal silicon, in addition tothe capsule geometries, allow the capsules to contain gas at a pressureof 17,500 psi. Other materials, such as diamond, could also be used toconstruct the capsules, including any of its components depending on thegas and the pressure to be contained within the capsules.

The single crystal silicon sealing lid that covers the fill/release portof a capsule is bonded to the capsule by anodic bonding (furtherdescribed below). This process produces a transition layer ofsodium-doped silicon dioxide (SiO₂) between the capsule and the lid. Thesodium-doped silicon dioxide can have bulk properties with respect totensile strength different from the crystal silicon. The sodium-dopedsilicon dioxide is a thin, e.g., on the order of, sub-micron layer, suchas an interfacial layer in thickness of joint material. The sodium-dopedsilicon dioxide is covalently bonded to both the crystal silicon of thecapsule body and the lid and completely fills surface roughness or voidsbetween the capsule and the lid. The transition layer can withstand thepressure within the capsule that pushes silicon lid outward and cannotbe extruded out from between the lid and the capsule body by the highpressure of the contained gas because of the very large length-to-heightratio of the layer (greater than 50 to 1). The transition layer also hasa low permeability to hydrogen molecules.

The slave control electronics 16 are applied onto the lids prior tobonding the lids to the capsules to seal the gases and can include asemiconductor circuitry, e.g., CMOS circuitry and metallization. Thematerials used allows these circuits to tolerate high temperatures,e.g., about 400° C. used in the anodic bonding process.

Processes for fabricating the DGS substrate 12 are now described indetail. As an overview, DGS capsule subcomponents (FIG. 11), the body 50a, 50 b, 50 c, the top caps 47, and the bottom caps 44, are made fromdifferent single crystal silicon substrates or wafers that areseparately processed. These capsule subcomponents are assembled to forma single “capsule subassembly” 55. In some embodiments, the body of thecapsule can be formed in more than one silicon substrate, which can bepre-assembled using, e.g., fusion bonding. The bottom caps are fusionbonded to one end of the cylinder body of the capsule, and the top capsare fusion bonded to the other end. In some embodiments, the bottom andtop cap pieces are attached to the silicon substrate containing thecylindrical capsule bodies at different times during assembly. Thecapsule components, including their subcomponents, may be assembled inother orders, Separately, a lid substrate 114 is constructed withactivation elements 38, X and Y addressing 32, 34 and electronic slavecontrol circuits 16. Subsequently in an high pressure assembly chamber,the capsules within the capsule subassembly are filled with a highpressure gas and sealed with the lid substrate 114.

DRIE (deep reactive ion etching) is one of several processes that may beused to fabricate the cylinder body or sidewalls of the capsules, aswell as, the gas fill/release ports/pathways. DRIE is a dry etch processand is suitable for forming features having an aspect ratio of up toabout 20:1 (e.g., the ratio of the depth and the width of the capsule onthe DGS device). Alternatively, the cylinders can be fabricated throughelectrochemical etching of a silicon substrate. The cylinders arefabricated by selectively etching cylindrical regions of a crystalsilicon substrate, as part of an electrochemical cell, to form poroussilicon regions in these cylindrical regions. After the porous siliconis formed in the cylindrical regions, the porous silicon may beconverted to silicon dioxide by exposing the porous silicon to oxygen atelevated temperature, and the silicon dioxide can be removed with anHydrofluoric acid (HF) dip while the crystal silicon in other regions ofthe silicon member remain substantially intact.

The fabrication processes may induce surface roughness on the walls ofthe formed capsules, which could adversely affect the tensile strengthof the material. It is desirable to take this factor into considerationwhen determining wall thickness between adjacent capsules and betweenadjacent sections 14. Alternatively, laser ablation can be used removesilicon material and to form the sidewalls of the capsules. High energylaser pulses, e.g., femto laser pulses or pico-second laser pulses, areapplied to selected locations of a silicon member to form capsules atthose locations. The dimensions and shapes of the capsules arecontrolled by controlling parameters associated with the ablation, e.g.,laser energy and duration of the process. Sidewalls of the capsules canbe formed quickly and precisely without substantially changing thecrystalline properties of the remaining silicon material.

The hemispherical bottom and top caps of the capsules are fabricatedusing wet etching. The fabrication scheme may optionally include formingpores at selected locations of a crystal silicon member. The poroussilicon at the selected locations, if implemented, acts as a gas flowthrottle. The silicon substrates containing the top and bottom caps canbe attached to the silicon substrate containing the cylindrical bodiesof the capsules by, for example, fusion bonding (also known as siliconwelding) to fully form the capsule subassembly 55 whose capsules areempty and unsealed. Generally, fusion bonding occurs in a chamber at ahigh temperature, e.g., about 1,000° C. and in a low pressure, suitablegas environment. The surfaces of the silicon substrates can be treatedto be smooth and clean to facilitate formation of the bonding betweenthem.

The fused silicon substrates containing the fully formed capsules(“capsule subassembly”) to be gas filled and sealed, are placed in ahigh pressure assembly chamber that will contain a hydrogen gas at about17,500 psi, as discussed below. The chamber is designed and built towithstand high pressures and is capable of holding a pressure up to,e.g., about 50,000 psi. The chamber heats the silicon capsulesubassembly and the separate lid silicon substrate to about 300° C. toabout 500° C., e.g., about 400° C. Then the two silicon pieces to beanodically bonded are arranged so that one piece has a voltage of about1,000 volts relative to the other piece. The high temperature and highvoltage bonds the silicon pieces together to form sealed capsules thatstore the high pressure hydrogen gas.

Referring to FIG. 8, capsules in which the hydrogen gas is stored aregas filled and sealed in a high pressure assembly chamber using aprocess 60. The assembly chamber is initially set up and in conditionfor use. A mechanical arrangement is provided for putting the lidsubstrate into position on the capsule subassembly once the assemblychamber is at a desired pressure (e.g., 17,500 psi). The assemblychamber is equipped with electrical connections to provide the voltagesused during the anodic bonding procedure and a heater element forheating the two silicon substrates.

In the set-up process 62, the silicon capsule subassembly and thesealing lid substrate are placed properly in the assembly chamber andthe assembly chamber is sealed. A nitrogen purge (64) process isperformed within the assembly chamber that removes oxygen from theassembly chamber by purging the assembly chamber with an inert gas, suchas nitrogen. Trapped air in the assembly chamber is displaced with theinert gas that does not substantially interfere with the processes to beperformed in the assembly chamber. In some embodiments, the nitrogenpurge process (64) is a pump-purge process including alternating stepsof pumping the chamber down to mild vacuum (e.g., 1 millitorr) andbackfilling with pure nitrogen. It is desirable to have substantially nooxygen in the assembly chamber during the high voltage anodic bondingprocess, e.g., for safety of the process. Removing air can alsofacilitate minimizing potential contamination of the hydrogen as thehydrogen gas is being sealed into the pressure capsules. After theassembly chamber has been thoroughly purged (e.g., of oxygen), thenitrogen is evacuated e.g., until the assembly chamber is in a lightvacuum. This evacuation procedure is performed so as not to dilute withnitrogen the gas that will fill the chamber next. It also preventsnitrogen from being trapped and compressed in the capsules.

A liquefied gas, e.g., a quantity of cryogenically condensed hydrogengas, e.g., that is pressurized and cooled to a very low temperature toexist in the liquid phase is introduced (66) into the assembly chamber.The liquid flashes to a gas as it warms thus pressurizing the assemblychamber. The amount of liquefied gas introduced into the chamber isselected such that the final gas pressure within the high pressureassembly chamber reaches a predetermined pressure, e.g., of 17,500 psiat ambient temperature. The amount of liquefied gas needed to beintroduced is calculated based on the total volume of the interior ofthe assembly chamber, the thermodynamic state of the cryogenic liquidand the final state at equilibrium temperature (ambient). The final gaspressure is controlled by adjusting the amount of liquefied gasintroduced into the assembly chamber and by controlled venting of highpressure gas, if needed. Filling the assembly chamber with the gas tothe desired pressure in the manner described above provides a relativelysimple and effective process to introduce hydrogen into the capsules ina efficient manner.. In other embodiments, compression equipment e.g.multistage compressors and hydraulic ram systems can pressurize gas tothe desired pressure.

The hydrogen gas enters the capsules due to the high pressure within theassembly chamber. The capsules are then sealed by the lid substrateusing an anodic bonding process within the assembly chamber. Again,without being bound by theory, it is believed that covalent bonds areformed between the silicon atoms in the lid silicon substrate and thetop caps of the capsules and the silicon oxide formed by the anodicbonding process.

The sealing process (68) begins with pressing the aligned capsulesubassembly 55 (FIG. 11) and lid substrate 114 together. Both siliconmembers are heated to approximately 400° C. A 1000 V voltage is appliedacross the two silicon members. The voltage accelerates the bondingprocess between the two silicon members and fills possible voids betweensurfaces of the members (e.g., due to surface roughness). A strong andgas tight seal can be formed. The press force is then released.

The sealed capsules containing the hydrogen gas are cooled down (70).The temperature in the assembly chamber is reduced to ambient. Theassembly chamber is depressurized (72). The residual hydrogen gas in theassembly chamber can be re-circulated back into a cryogenic system orsafely vented.

After the process 60 has been completed, the substrates carrying thecapsules are diced into a predetermined size according to the needs of aspecific application and integrated into the DGS device 10 of FIG. 2. Inuse, the DGS device 10 of FIG. 2 is placed within an enclosure 11 (FIG.2) that serves as a gas chamber. The gas chamber collects gas releasedby the DGS device and also prevents gases outside the gas chamber fromentering the DGS device. The gas released from the DGS device into thegas chamber is supplied to a device, e.g., a fuel cell, coupled to thegas chamber. The control chip substrate 20 of FIG. 2 monitors thepressure in the gas chamber in order to know when to instruct the DGSdevice to release more gas. In some embodiments, the control chipsubstrate 20 of FIG. 2 can be included within the chamber 11 and inothers it is external to the chamber 11, as shown in FIG. 2. In someembodiments to facilitate gas flow from the DGS device 10 when sections14 are ruptured the substrates 12 can have one or a plurality ofgrooves, e.g., V-shaped grooves or other similar types of channels (invarious configurations not shown) fabricated on the back sides of thesubstrates.

The gas released initially from the DGS device 10 expands to the volumeof the gas chamber, which has an ambient pressure and temperature. Giventhe fixed volume of the gas chamber, the gas released later from the DGSdevice 10 can increase the pressure within the gas chamber. In someembodiments, the gas chamber includes an accumulator to prevent thepressure from rising above a predetermined value (e.g., 1 psi). Theaccumulator has a collapsed state in which the volume is small, and anexpanded state to accommodate an increased pressure. In use, theaccumulator expands to accommodate the volume of the recently releasedgas to prevent the pressure of the gas chamber from risingsignificantly. The volume of the accumulator is affected by the amountof gas released from the DGS device and the shape is variable based onspecific applications. The accumulator may be integrated into the gaschamber.

Referring back to FIG. 2, a three-wire communication interface scheme isbuilt between each DGS substrate 12, e.g., the slave control electronics16 and the master control chip substrate 20. The substrates 12, 20 maybe electrically connected in serial or parallel. Two types of signalsare used by the interface, corresponding to power and information,respectively. The power signals include a −V signal, e.g., sent from theelectrode or conductor 28 on the control substrate 20. The −V signal canserve as a reference signal to the information signal and also as a sinkto the current source. The power signals also include a +V signal viathe electrode or conductor 26 that sources the current to the selectedthermal activation element 38 of FIG. 3A.

Referring to FIG. 9, the control substrate 20 includes circuits 78 thatmonitor and manage gas release from the DGS device 10. A power circuit80 can be included on the control substrate 20 to provide power to thecircuits 78 and deliver power via electrodes or conductors 26, 28 tocontrol the slave circuits 16 on each of the DGS substrates 12. Otherarrangements to provide power to the control circuits 78 and 16 arepossible and include voltage regulation of the power circuits. Thecircuits 78 include an X row counter 84, a Y column counter 86, and asubstrate counter 88. The circuits 78 use the substrate counter 88 toselect a particular substrate 12, and use the X row and Y columncounters 84, 86 to select a particular section 14 on the particularsubstrate 12. Any section 14 in the DGS device can be located using thethree counters 84, 86, 88.

The circuits 78 also include a clock circuit 90. Clock information ismodulated with X, Y addressing data and substrate and sent to thecontrol electronics 16. The modulated clock and data information aretransmitted from a parallel to serial converter circuit 92, in whichparallel data and clock information corresponding to an X row count anda Y column count and substrate is converted into a serial stream of dataand embedded clock information. Based on the address of a selection bythe counters 84, 86, 88, the data and clock information is deliveredfrom the circuit 92 through a data line 30 (see also, FIG. 2) to thedecode circuits and then to the selected section 14 to release the gasstored in the section 14.

The control substrate 20 can also include a pressure sensor circuit 96that has a predetermined pressure threshold and outputs signal toindicate a low pressure when sensed pressure is lower than the pressurethreshold. The pressure sensor circuit 96 can be used to initiate gasrelease from one or more particular sections 14 to maintain the pressurein the gas chamber in which the control chip substrate 20 is located.

In addition, the control substrate 20 includes a sleep mode circuit 98.When consumption of the released gas decreases or stops, the sleep modecircuit 98 interacts with the circuits 78 to make the DGS system 22 toenter the sleep mode (described below). It is desirable to prevent ahigh gas pressure from being applied to the control substrate 20 whenthe high pressure is not needed, so that no excessive amount of gas issupplied to the external gas consuming device. For example, the hydrogenmolecules tend to permeate membranes used in a fuel cell that consumesthe hydrogen gas, and excessive hydrogen gas provides a high pressurethat may accelerate the permeation.

The information signals carry clock and data information. The clockinformation and the data information are modulated together so that onlyone wire is used (referenced to the −V signal). The data informationincludes a substrate count, an X row count and a Y column count, and arestored and managed on the control chip substrate 20. Other schemes canbe used to allow the use of a single pulse (clock) that advances thelocal counters on each substrate. Each local counter can be enabled by acarry in/out signal daisy chained between DGS substrates. Other schemesfor communication among the control chip substrate 20 and the DGSsubstrate 12 can be used.

A pressure sensor in the gas chamber, in which the DGS device 10 isplaced, automatically monitors the gas pressure of the gas chamber anddelivers information about demand for gas to the control chip. Thepressure in the gas chamber is used to determine when to release thenext quantity of gas. The process of gas release can continueuninterrupted until the DGS device 10 is out of gas. In someembodiments, the gas release can be suspended if the external gasconsuming device stops, suspends, or substantially decreases consumptionof the released gas and the DGS system 22 goes into a sleep mode. In thesleep mode, the amount of gas that is being used is substantially lessthan the normal operational state. In the sleep mode, the gas isreleased at a lower pressure so there is less leakage through thecontrol chip, and/or it is released at greater intervals because thereis less consumption. In some embodiments, the substrates 12 includespecial sleep mode capsules that store smaller amounts of gas to produceless pressure in the gas chamber when these sleep mode capsules releasegas.

Referring to FIG. 10, the DGS slave control electronics 16 on each DGSsubstrate 12 (FIG. 1A) decodes the data and clock information sent bythe control circuits 78 of FIG. 9. The serial data and clock informationis received at a serial/parallel convert circuit 100, which demodulatesthe information to recover the data and converts the serial data backinto a parallel format.

In an example in which the selected substrate 12 includes 100 (10×10)sections 14, the X row and Y column data is decoded to a one of tenselect lines each using an X row decoder 102 and a Y column decoder 104.The selected row Xn is connected to a current source 106 and theselected column Ym is connected to a sink driver circuit 108,respectively. The current source 106 and the sink driver circuit 108deliver current to a thermal activation element 38 that has an addressedof (Xe, Ym) within the matrix of thermal activation elements on eachsubstrate 12. Additionally, data related to the selection of thesubstrate 12 is also decoded, which is compared to a local substrate IDnumber. When a substrate 12 having a particular ID number is selected, asubstrate enable signal turns on a power switch (not shown) to supply acurrent to the X_(n). When no substrate is selected, no current flow isdelivered to heat the selected thermal element at the address (X_(n),Y_(m))

Referring to FIG. 11, a cross-sectional view of a portion of the DGSsubstrate 12 includes sections 14 of capsules 14 a, 14 b, . . . ,arranged in a cascade configuration. Each capsule 14 a, 14 b, . . . , isseparated from other capsules by rupturable walls 112. As indicated bythe solid horizontal lines, the DGS substrate 12 is formed from multiplesilicon members 44, 50 a, 50 b, 50 c, 47 and lid 114 stacked upon oneanother and bonded to each other. The sections 14 of capsules are eachseparated by thick walls 110 that are structured to limit the cascaderupture to an activated section 14 of capsules, thus preventing thenon-activated adjacent sections from rupturing.

Referring now to FIG. 12A, a top area of the capsules of FIG. 11 in thecircled area A is shown in detail. The top caps 46 i, 46 j, 46 k of thecapsules 14 i, 14 j, 14 k include gas fill ports 40 covered by a thinlid 114. A thermal activation element 38 is in contact with the thin lid114 and can be located above the center of one or more ports 40. Therupturable walls 112 each can be relatively thin and can have athickness of about 0.8 micron to about 1.2 microns.

Referring to FIG. 12B, a bottom area of the capsules 14 m, 14 n aresealed by the bottom caps 42 m, 42 n. The wall 110 separating capsules14 m, 14 n from different sections 14 can have a relatively largethickness, for example, about 20 to about 50 microns.

The DGS system 22 (FIG. 2) has a small size and is lightweight. Thehydrogen gas stored in the DGS device 10 of the DGS system 22 has a highenergy density, for example, a high gravimetric energy density. The DGSsystem 22 or DGS device 10 may be suitable for use in lightweight,portable applications, e.g., micro autonomous sensors and robots, suchas small flying robots, and portable electronics, such as cell phones.

In addition to the control substrate 20 producing power, the controlsubstrate 20 eliminates or reduces the amount of onboard electronicsgenerally associated with power and power management for the abovementioned application. The control substrate 20 accomplishes this byintegrating the circuits and software needed to control the controlelectronics 16 on each substrate 12. The power functions can not only bemonitored and controlled but also adjusted dynamically to real timesituations and events.

In addition to providing a substantial amount of stored energy on amicro level, the DGS device/system can also be used to perform otherfunctions. For example, the DGS device/system may be used to store anantidote. When needed, e.g., during a combat situation, terroristattack, health crisis or when a bio threat is detected, the DGSdevice/system can be activated and the antidote can be released from thecapsules. The pressure in the capsules may be used to inject theantidote directly into a subject or release the antidote as an aerosol.Generally, the DGS device/system can be used to release a combination ofmaterials as an injection or aerosol.

The DGS device/system can have other uses. In one example, the DGSdevice/system can propel items such as a dart. In another example, theDGS device/system may be used in connection with a reconnaissancedevice, such as a small flying robot, to target and deploy a directedprojectile device, such as a dart. The projectile may be chemicallytreated for various desired effects. The projectile may include one ormore sensors so that the propulsion mechanism of the DGS device/systemcould also be used to deploy sensors.

In another application, the DGS device 10 may store different gases indifferent sections or capsules. For example, H₂ and O₂ can be stored inseparate capsules for use in circumstances where no or low quality airexists or under water. If an external gas consuming device coupled tothe DGS device/system is expected to encounter poisonous or contaminatedair during its operation, the gas consuming device may be configured tocarry reactants. The oxygen provided by the DGS device/system wouldallow the gas consuming device to function both on land and under waterand in space. In some applications, the DGS device/system may providebuoyancy control to small underwater autonomous vehicles.

Alternatively, the DGS device 10 may store vacuum. In this application,the gas is removed from the capsules and the capsules are then sealed tocreate instances of vacuum. When one capsule or a section of capsulesare activated, external gases or liquids can flow into the capsules toquench the vacuum. The selection of sections of vacuum based on theaddresses of the sections are similar to a digitally controlled vacuum.The precise control of which section of vacuum to be activated can beused to invoke a gas or a liquid to flow through an external flowcircuit connected to the DGS device.

The thermal activation element 38 can have other configurations. Otherthan the thermal activation elements 38, other activation elements,e.g., magnetic activation elements, can be used together with or inreplacement of the thermal activation elements 38. The capsules can havedifferent shapes, for example, an oval, square, or triangular crosssection. One or more parts of the capsules can be formed in the samesilicon member. For example, the bottom caps and the bodies of thecapsules can be formed in the same silicon member.

The control circuitry can be implemented in digital electroniccircuitry, or in computer software, firmware, or hardware, such as logiccircuitry, including counters, state-machines, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.

For example, other materials could be substituted or used in addition tothe ones described for the DGS device and any of its components. Otherdimensions and configurations, including the number of capsules persection, the number of section per DGS substrate, and the arrangement ofsections, the sizes of the capsules, in addition the ones alreadydescribed previously could be used. The DGS device may be used for anygas, including but not limited to: hydrogen, oxygen, and a mixture ofgases, such as air. The DGS device may also store vacuum as describedabove.

Other fabrication processes may be used in place or in additional to theprocesses described above. Other embodiments are within the scope of thefollowing claims.

1. A gas storage system comprising: a first substrate having plural groups of capsules formed within the first substrate, with each of the capsules containing gas stored at a relatively high pressure compared to atmospheric pressure; a plurality of activation elements, each one coupled to a corresponding one of the plurality of groups, the activation element configured to deliver energy in an amount sufficient to cause at least one of the capsules each of the plurality of groups to release stored gas; a second substrate having a second plurality of groups of capsules formed within the second substrate, with each of the capsules of the second plurality of groups of capsules containing gas stored at a relatively high pressure compared to atmospheric pressure; and a second plurality of activation elements, each one coupled to a corresponding one of the second plurality of groups, the activation element configured to deliver energy in an amount sufficient to cause at least one of the capsules in the second plurality of groups of capsules to release stored gas.
 2. The gas storage system of claim 1 further comprising: control electronics coupled to the activation elements, the control electronics configured to selectively deliver electrical signal to control operation of a selected one of the activation elements.
 3. The gas storage system of claim 1 wherein the capsules are interconnected by channels that allow gas to flow between the capsules, the capsules configured to release the gas simultaneously when at least one of the capsules is activated by the activation element.
 4. The gas storage system of claim 1, wherein the capsules are discrete elements positioned adjacent to each other, the capsules having a wall thickness selected to be sufficient to hold a predetermined storage pressure only when the capsules are positioned adjacent to each other, wherein a rupture of one of the capsules causes a cascading rupture of the remaining capsules of the group.
 5. The gas storage system of claim 1 wherein the material of the substrate is single crystalline silicon.
 6. (canceled)
 7. The gas storage system of claim 1, wherein the first and second substrates are part of a plurality of substrates, with each of the plurality of substrates further comprising: groups of gas filled capsules therein and corresponding activation elements for the groups of the capsules, the activation elements configured to deliver energy in an amount sufficient to cause at least one of the capsules in each group to release stored gas; and control electronics coupled to the activation elements. 8-11. (canceled)
 12. The as storage system of claim 7, wherein the system comprises: gas channel substrates interposed between pairs of substrates of the plurality of substrates; a first lid substrate that is anodically bonded to a first one of the substrates of the plurality of substrates; and a second lid substrate that is anodically bonded to a last one of the substrates of the plurality of substrates.
 13. A system for digitally controlled release of a fluid, the system comprises: a plurality of substrates arranged in a stack of substrates, with each substrate including: groups of fluid-filled capsules coupled to activation elements; and control circuitry configured to deliver a control signal to a selected activation element, the control signal causing the selected activation element to rupture a corresponding group of fluid-filled capsules to release fluid in the corresponding group.
 14. The system of claim 13 wherein the fluid is a gas contained at a relatively high pressure compared to atmospheric pressure.
 15. The system of claim 13 wherein the capsules are micro pressure vessels.
 16. The system of claim 13 wherein the capsules are micro pressure vessels, and are arranged in groups each group configured to allow fluid to flow between the capsules within that group, such that the capsules with the group release the fluid simultaneously when at least one of the lids of a capsule in that group is ruptured by the activation element.
 17. The system of claim 13 wherein the capsules are discrete elements packed adjacent to each other, the capsules having a wall thickness selected to be sufficient to hold a predetermined storage pressure only when the capsules are positioned adjacent to each other, wherein a rupture of one of the capsules causes a cascading rupture of the remaining capsules of the group.
 18. The system of claim 13 wherein the material of the substrate is single crystalline silicon.
 19. The system of claim 13 wherein the group of capsules are arranged in a hexagonal packing.
 20. The system of claim 13 wherein the fluid is an elemental gas and each of the plurality of substrates are comprised of crystalline material selected from the group consisting of silicon, diamond and materials that have sufficient tensile strength to withstand pressure of gas in the micro-capsules. 21-26. (canceled)
 27. The system of claim 13 wherein the fluid is a gas, and the system further comprises: the controller for controlling operation of the gas storage system, the controller comprising: logic circuitry to select a group of gas-filled capsules fabricated within a substrate, the circuitry comprising: circuitry to determine an address for the group, including an row count and a column count; and circuitry to determine a substrate count that corresponds to the group of gas filled capsules.
 28. The controller of claim 27, further comprising: circuitry to deliver control signals sufficient to cause the activation element to produce energy in an amount sufficient to release gas from the groups of capsules.
 29. The controller of claim 27, further comprising: a sensor configured to monitor gas pressure.
 30. The controller of claim 29 wherein the logic circuitry is further configured to adjust a number of subsequent groups selected for activation based on the monitoring.
 31. The controller of claim 29 wherein the logic circuitry is further configured to adjust a frequency of selection of subsequent groups for activation based on the monitoring.
 32. (canceled) 